1. Field of the Invention
The present invention relates to a solid-state imaging apparatus and a reading method used in the imaging apparatus.
2. Description of the Related Art
A conventional method for increasing the dynamic range in a solid-state imaging apparatus is disclosed: signals accumulated in photosensors are read at different times and are separately and directly transferred to the exterior by the use of a charge-coupled device for reading all of the pixels rather than being mixed with each other in vertical registers. The signals are then added in the exterior.
Another known method for increasing the dynamic range is also disclosed: a filter is formed on photosensors so that some photosensors can possess higher sensitivity and some photosensors possess lower sensitivity. The signals are thus read from the photosensors having the adjusted sensitivity, and are then added horizontally or added in the exterior. The solid-state imaging apparatus using this method can be manufactured with a process similar to that of the solid-state imaging apparatus employing the inter-line transfer method, which is typically used. Thus, the manufacturing cost of this method is less expensive than that of the previous method. This method is also advantageous over the previous method because it can use a signal processing circuit similar to that of the inter-line transfer method.
The above-described conventional methods, however, present the following problems. The former known method requires a charge-coupled device for reading all of the pixels, thereby increasing the manufacturing cost. A line memory is also needed resulting in complicated signal processing. In the latter method, since the attenuation of transmitted light takes place by the provision of a filter, the magnification factor of the dynamic range is fixed or not variable, and also, the substantial sensitivity is lowered due to the provision of a filter.